There were three formations known as the Army of Mississippi in the Confederate States Army during the American Civil War.
This army, at times known by the name Army of the West was one of the most important in the Western Theater, fighting at Shiloh, Corinth, and Perryville.
On November 20, 1862, it was renamed the Army of Tennessee.
It was organized December 7, 1862, by troops in the Department of Mississippi and East Louisiana, including the short-lived Army of West Tennessee.
It ceased to exist when southern General John C. Pemberton surrendered it after a long offensive campaign and siege to Major General Ulysses S. Grant on July 4, 1863, opening up the "Father of Waters" to Union control and splitting the Confederacy in two.